There are a variety of electrically driven systems that require one or multiple sources of high voltage AC power for controlling the operation of one or more system application devices. As a non-limiting example, a liquid crystal display (LCD), such as that employed in desktop and laptop computers, or in larger display applications, such as large scale television screens, requires that an associated set of high AC voltage-driven cold cathode fluorescent lamps (CCFLs) be mounted directly behind it for backlighting purposes. Where the LCD panel is a large scale display device, a relatively large number (e.g., on the order of twenty to forty) of such lamps is required to achieve uniform backlighting.
In order to obtain a uniform brightness output from all such lamps (and therefore uniform backlighting of the LCD display), it is common practice to have the output of a respective one of a plurality of inverter circuits (voltage-controlled switching devices and associated output transformers coupled to the lamps) coupled to a prescribed number of (e.g., on the order of four to five) CCFLs, and drive each inverter circuit by way of a common high frequency switching signal (such as a 50 KHz signal). Unfortunately, as the number of inverter circuits is increased (in association with larger area CCFL backlighting requirements), the larger is electromagnetic interference (EMI) produced by driving multiple inverter circuits with the same switching signal. Indeed, for relatively large power switching systems, the magnitude of the EMI may be so large as to make the system non-compliant with FCC specifications.